Today, image-based inspection systems are often employed for physical inspection of an object of interest. Such systems typically employ an optical- or x-ray-based source at a distance from an object of interest at which an area of the object is in focus. Additionally, many such systems currently employ a positioning mechanism whereby the distance between the imaging source and the object is adjustable so that the area of the object to be inspected may be brought into proper focus.
For example, x-ray laminography machines that are employed to inspect printed circuit boards (PCBs) for manufacturing defects often utilize such a mechanism to keep a portion of the board under inspection within a narrow focal plane. That focal plane represents a thin xe2x80x9cslicexe2x80x9d of the PCB under inspection, allowing a view of a limited depth within the PCB. Such a view provides an advantage over typical transmissive x-ray inspection systems, which do not employ a focal plane, thus providing a view of all components and interconnections simultaneously, making analysis of the physical aspects of the PCB difficult. The position of the focal plane is determined by the location of an x-ray source and x-ray detector, which reside on opposite sides of the PCB under inspection. The area under inspection at any one time, which is normally termed a field of view, is roughly square in shape, and is typically much smaller than the area of the PCB itself. Consequently, the PCB is viewed in increments, section by section, layer by layer, until all areas of interest are inspected.
Unfortunately, warping of the PCB may be of sufficient severity that some portion of an area being inspected at any one time may remain out of focus, forcing the use of an even smaller inspection area. As seen in FIG. 1, a warped PCB 100 may cause all but a small area on the top side of PCB 100 to reside outside of a depth of focus 110 of an optical or x-ray inspection system, resulting in a small area, defined by a narrow width 120, that may be inspected at any one time. The use of a reduced inspection area generally results in more inspection areas being necessary for each PCB, thereby resulting in a significantly longer inspection time required for each PCB and, consequently, a drastic reduction in PCB inspection throughput.
Additionally, the focus problems due to PCB warping can also cause the inspection system to falsely identify out-of-focus areas of the PCB under inspection as manufacturing defects, resulting in costs due to unnecessary additional testing or discarding of properly manufactured PCBs.
Such problems regarding a changing focal distance over the surface of an object are not limited to PCB x-ray laminography inspection machines. Other optical- or x-ray-based viewing or inspection machines that employ only a focal length adjustment likely encounter the same difficulties with objects having a nonplanar structure to be viewed or inspected.
Therefore, from the foregoing, a new image-based inspection system that allows more area of an object under inspection to reside within the depth of focus, thus allowing for a greater inspection area and, thus, higher inspection throughput, would be advantageous.
Embodiments of the invention, to be discussed in detail below, allow the relative position between an object under inspection and the focal plane of an image-based inspection system to be altered by way of translation and rotation so that more of the object will reside within the focal plane. Continuing with the PCB example in FIG. 2, if the warped PCB 100 (from FIG. 1), or the imaging source/detector pair, is translated and rotated in a certain way, more area of the top surface of PCB 100, as defined by larger width 200, lies within depth of focus 110. Since warping or other irregularities in an object under inspection can occur in any direction along a surface of the object, the ability of an image-based inspection system to translate and rotate either the object or the imaging system to properly align the object with the focal plane is desirable.
An image-based inspection system according to an embodiment of the invention includes, in part, means for imaging a portion of an object under inspection. As noted earlier, the imaging means provides a focal plane that allows the viewing of a figurative xe2x80x9cslicexe2x80x9d of the object. To allow more of an area of interest within the object to be viewed, means for altering the relative position of the focal plane of the imaging means and the object is provided. The positioning altering means manipulates the translational location and rotational orientation of the object or the imaging means. Also included is means for mapping part of the surface of the object, thereby generating a representation of that part of the surface of the object. A means for controlling the operation of the manipulating means then utilizes the surface representation so that the portion of the object being inspected lies substantially within the focal plane of the imaging means. Optionally, means for automatically interpreting the image from the imaging means is included.
Another embodiment of the invention exists in the form of a method of image-based inspection of an object, with a portion of the object to be inspected being required to lie within a focal plane in order to be imaged. First, at least part of the surface of the object is mapped so that a representation of that part of the surface of the object is generated. Next, the translational position and rotational orientation of either the object or the narrow focal plane is altered based on the surface representation so that the portion of the object being inspected lies within the focal plane. That portion of the object is then imaged for inspection purposes. Optionally, the resulting image may then be automatically interpreted to determine the status or quality of the object.
Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.